1. Technical Field of the Invention
The present invention relates to ball mill grinding devices and methods, in general, and, in particular, to batch ball mill grinding devices and methods.
2. Description of Related Art
Ball mills are well known in the art and are commonly used in laboratories and in industry for the purpose of rapidly and without loss grinding and mixing materials.
One known type of ball mill is commonly referred to as a centrifugal mill. A material to be ground, together with balls of another, hard material, are inserted into a cylindrical vessel. This vessel is then revolved about its axis (or perhaps an axis offset therefrom) at a predetermined speed of rotation to cause movement of the balls within the material. The action of the accelerating forces of the moving balls resulting from vessel rotation causes grinding or mixing of the material. It is important with centrifugal ball mills to carefully control the velocity of rotation because, for each material to be ground or mixed in a given diameter vessel, there exists a limiting value of the rate of rotation beyond which the balls will remain stationary against the inside wall of the vessel and fail to effectuate any grinding action.
By orientating the axis of rotation horizontally, gravitational forces may be used in addition to rotational forces to cause cascading ball movement resulting in an improvement to the grinding or mixing effect. These horizontally oriented centrifugal ball mills are also known as tumbling mills. In this configuration, the material is ground or mixed as a result of compressive collapse and frictional abrasion due to gravitational drop of the cascading balls.
To counter agglomeration effects within the vessel and enhance the homogenization of the material, the direction of rotation for the vessel in a centrifugal ball mill may be reversed.
Another known type of ball mill is commonly referred to as a planetary ball mill. A plurality of mill pots receive a material to be ground together with balls of another, hard material. Each mill pot is mounted to an independently rotatable platform. The plurality of pots are evenly disposed around a main axis of rotation. As the plurality of pots are rotated about the main axis in one direction, each of the individual pots independently rotates about its own axis in an opposite direction. This “planetary” action causes centrifugal forces to alternately add and subtract. Interaction with the material occurs as the balls within each pot roll halfway around the pot and are then thrown across the pot. The synergistic effect between centrifugal forces due to revolution and rotation, combined with the Coriolis force, results in improved grinding/mixing in comparison to centrifugal ball mills.
The need for high volume and quick grinding and sample preparation is well recognized in connection with the primary chemical analysis of many materials, for example, seeds and plant tissues. This chemical analysis is typically performed in connection with the screening of seeds and plant tissues for certain desirable traits. Given the number of seeds and plant tissues a scientist or breeder must screen, and the limited amount of time available for completing such screenings, it is important that seeds and plant tissues be quickly ground to speed the overall analysis operation to identify and select seeds and plants of interest. It is also vitally important to maintain sample isolation and thus ensure that the ground seed or tissue for one sample does not contaminate another sample. Known and readily available ball mill devices do not possess the ability to quickly grind seeds and tissues in the volumes, and with the requisite isolation, needed by scientists and breeders.